Programming languages are simply a problem of learning syntax and the build environment. Scan through a couple of books, maybe read a specification, write some code, and you got it.

The hard stuff is problem solving, understanding algorithms and their applicability, implementing and using data structures, how computers work, how they represent types and resources, how networks work, network protocols, databases, processes, threading, asynchronous coding etc. All of this knowledge is mostly independent from programming language and platforms and will apply from one language to another. Learning the syntax of a programming language is trivial when compared to other programming topics.

If Ruby and Ruby on Rails dies tomorrow or Python and Django or whatever, and you know of the things I just mentioned picking up the next thing should be not be a difficult task. I don't really care what language someone already knows when it comes to hiring. If you don't know JavaScript, but you know Ruby or Java or C#, and you understand Computer Science, have demonstrated being able to write working code and are not afraid to ask questions picking JavaScript on the job is OK with me. We'll do code reviews, explains things, get you going.

>The hard stuff is problem solving, understanding algorithms and their applicability, implementing and using data structures, how computers work, how they represent types and resources, how networks work, network protocols, databases, processes, threading, asynchronous coding etc.

Yeah, and knowing which libraries to use to do all that stuff and what quirks they have.

That type of knowledge doesn't translate overnight between programming ecosystems. It takes years.

It takes years because you learn about these things as you go, and you solve them as you go and by looking at the source code of things you're using. People started using and jumping right into scala, and go and and node.js, solving the problems as they ran into them because they had the skill to do so.

Yet it still takes years.

It's almost worse when the stack is new because there is so much of the wheel that has to be reinvented again.

Not a recipe for learning to write idiomatic code in any new language. (I mostly hear of C++ programmers that really only write C).

There is no such thing as JavaScript as an employable skill. It's all about the framework.

Give it time, and someone will write a Ruby/Python to JS pre-processor in JS.

Drats, as I was writing this, someone did:

http://opalrb.org/